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Date: Sun Feb 27 13:22:22 2005

Address lines A0 to A11 go to the PROM array (it is a 4K card, right?)

Address lines A12 to A15 go to the card selection logic where they're
compared with the setting of the DIP switch. Switch A1 corresponds to
address line A12 ... Switch A4 corresponds to A15 and a switch that's on
corresponds to a 0 on the address line. So if, for example, switches A3
and A4 are on, then the address lines must be in the states

A15 = 0 (becasue A4 is on)
A14 = 0 (because A3 is on)
A13 = 1 (because A2 is off)
A12 = 1 (because A1 is off)

So the card responds to addresses in the range 3000 to 3FFF

> Why would the address lights on the Altair not properly
> correspond to the address switches being set? If I set the
> switches at 1110111000000000, for instance, when I reset
> then examine the light at A11 doesn=92t come on (the lights
> show 1110011000000000) even though I know that LED to be
> functioning.

If I am looking at the right schematics, then the address LEDs are driven
from the S100 address lines by an inverter and buffer each. So either the
driver chips are faulty or address line A11 is never going high. This
could be a short on the bus, or it could be a problem with the CPU card I

> Why would the data lights ever show anything but on or off?
> I sometimes get dim glows from the data LEDs.

If the machine is running a program then the data lines will be changing
too fast to see. The LED will sometimes be on and sometimes off, but it
will appear as a dimmer light.

> What data can I expect to be in the RAM on boot-up? Is this
> answer different for Static vs. Dynamic RAM?

Random. Don't assume anything is there. Some RAMs seem to start up with
roughly the same pattern of data each time, but don't depend on it.

Received on Sun Feb 27 2005 - 13:22:22 GMT

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